Header Error Control Protected Ten Gigabit Passive Optical Network Downstream Frame Synchronization Pattern

ABSTRACT

An apparatus comprising an optical line terminal (OLT) configured to couple to a plurality of optical network units (ONUs) and transmit a plurality of downstream frames to the ONUs, wherein each of the downstream frames comprises a plurality of forward error correction (FEC) codewords and a plurality of additional non-FEC encoded bytes that comprise synchronization information that is protected by Header Error Control (HEC) code. An apparatus comprising a processing unit configured to arrange control data, user data, or both into a plurality of FEC codewords in a downstream frame and arrange a physical synchronization sequence (PSync), a superframe structure, and a Passive Optical Network-identifier (PON-ID) structure in a plurality of additional non-FEC encoded bytes in the downstream frame, and a transmission unit configured to transmit the FEC codewords and the additional non-FEC encoded bytes in the downstream frame within a 125 microsecond window.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. patent application Ser.No. 12/884,566, filed Sep. 17, 2010 filed by Yuanqui Luo, et al., andentitled “Header Error Control Protected Ten Gigabit Passive OpticalNetwork Downstream Frame Synchronization Pattern,” which claims priorityto U.S. Provisional Patent Application 61/287,024, filed Dec. 16, 2009by Yuanqiu Luo, et al., and entitled “HEC Protected XG-PON1 DownstreamFrame Sync Pattern,” both of which are incorporated herein by referenceas if reproduced in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

A passive optical network (PON) is one system for providing networkaccess over “the last mile.” The PON is a point to multi-point networkcomprised of an optical line terminal (OLT) at the central office, anoptical distribution network (ODN), and a plurality of optical networkunits (ONUs) at the customer premises. In some PON systems, such asGigabit PON (GPON) systems, downstream data is broadcasted at about 2.5Gigabits per second (Gbps) while upstream data is transmitted at about1.25 Gbps. However, the bandwidth capability of the PON systems isexpected to increase as the demands for services increase. To meet theincreased demand in services, some emerging PON systems, such as NextGeneration Access (NGA) systems, are being reconfigured to transport thedata frames with improved reliability and efficiency at higherbandwidths, for example at about ten Gbps.

SUMMARY

In one embodiment, the disclosure includes an apparatus comprising anOLT configured to couple to a plurality of ONUs and transmit a pluralityof downstream frames to the ONUs, wherein each of the downstream framescomprises a plurality of forward error correction (FEC) codewords and aplurality of additional non-FEC encoded bytes that comprisesynchronization information that is protected by Header Error Control(HEC) code.

In another embodiment, the disclosure includes an apparatus comprising aprocessing unit configured to arrange control data, user data, or bothinto a plurality of FEC codewords in a downstream frame and arrange aphysical synchronization sequence (PSync), a superframe structure, and aPassive Optical Network-identifier (PON-ID) structure in a plurality ofadditional non-FEC encoded bytes in the downstream frame, and atransmission unit configured to transmit the FEC codewords and theadditional non-FEC encoded bytes in the downstream frame within a 125microsecond window.

In yet another embodiment, the disclosure includes a method comprisingimplementing, at an ONU, a synchronization state machine that comprisesa Hunt State, a Pre-Sync State, and a Sync State for a plurality ofdownstream frames, wherein each of the downstream frames comprises aphysical synchronization block (PSBd) comprising a Physicalsynchronization (PSync) pattern, a superframe structure, and a PON-IDstructure, wherein the superframe structure comprises a superframecounter and a first HEC protecting the superframe structure, and whereinthe PON-ID structure comprises a PON-ID and a second HEC protecting thePON-ID structure.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a schematic diagram of an embodiment of a PON.

FIG. 2 is a schematic diagram of an embodiment of a frame.

FIG. 3 is a schematic diagram of an embodiment of a portion of a frame.

FIG. 4 is a schematic diagram of another embodiment of a portion of aframe.

FIG. 5 is a schematic diagram of an embodiment of a synchronizationstate machine.

FIG. 6 is a flowchart of an embodiment of a PON framing method.

FIG. 7 is a schematic diagram of an embodiment of an apparatusconfigured to implement a PON framing method.

FIG. 8 is a schematic diagram of an embodiment of a general-purposecomputer system.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

In PON systems, errors in a plurality of frames may be corrected using aFEC scheme. According to the FEC scheme, the transmitted frames maycomprise a plurality of FEC codewords, which may comprise a plurality ofdata blocks and parity blocks. Each quantity of blocks that correspondto an FEC codeword may then be aligned or “locked” using a “statemachine,” e.g. in a buffer, framer, or memory location at an ONU or OLT.The FEC codeword may be locked after detecting one by one its datablocks and parity blocks and verifying that the blocks' sequence matchesthe expected block sequence of an FEC codeword. Otherwise, when a blockis detected as out of sequence, the process may be restarted at thesecond block in the block's sequence to detect and lock the correctblock sequence.

Disclosed herein is a system and method for supporting transmissionsynchronization and error detection/correction in PON systems, such as10 Gigabit PONs (XGPONs). The system and method uses a framing mechanismthat supports the FEC scheme and provides transmission synchronizationin the PON. The frames may be transmitted within a plurality oftransmission windows, e.g. about 125 microseconds time periods, whereeach transmission window may comprise an integer multiple of FECcodewords for error detection/correction. The transmission window mayalso comprise additional or extra bytes that may be used fortransmission synchronization. The extra bytes may comprise framesynchronization and/or time synchronization and may not be FEC encoded(e.g. not protected by FEC), and therefore may not be handled by the FECscheme. Instead, the extra bytes may also comprise HEC encoding, whichmay provide error detection/correction for the synchronizationinformation in the frames.

FIG. 1 illustrates one embodiment of a PON 100. The PON 100 comprises anOLT 110, a plurality of ONUs 120, and an ODN 130, which may be coupledto the OLT 110 and the ONUs 120. The PON 100 may be a communicationsnetwork that does not require any active components to distribute databetween the OLT 110 and the ONUs 120. Instead, the PON 100 may use thepassive optical components in the ODN 130 to distribute data between theOLT 110 and the ONUs 120. The PON 100 may be NGA systems, such as tenGigabit GPONs (or XGPONs), which may have a downstream bandwidth ofabout ten Gbps and an upstream bandwidth of at least about 2.5 Gbps.Other examples of suitable PONs 100 include the asynchronous transfermode PON (APON) and the broadband PON (BPON) defined by theInternational Telecommunication Union Telecommunication StandardizationSector (ITU-T) G.983 standard, the GPON defined by the ITU-T G.984standard, the Ethernet PON (EPON) defined by the Institute of Electricaland Electronics Engineers (IEEE) 802.3ah standard, the 10 Gigabit EPONas described in the IEEE 802.3av standard, and the Wavelength DivisionMultiplexed (WDM) PON (WPON), all of which are incorporated herein byreference as if reproduced in their entirety.

In an embodiment, the OLT 110 may be any device that is configured tocommunicate with the ONUs 120 and another network (not shown).Specifically, the OLT 110 may act as an intermediary between the othernetwork and the ONUs 120. For instance, the OLT 110 may forward datareceived from the network to the ONUs 120, and forward data receivedfrom the ONUs 120 onto the other network. Although the specificconfiguration of the OLT 110 may vary depending on the type of PON 100,in an embodiment, the OLT 110 may comprise a transmitter and a receiver.When the other network is using a network protocol, such as Ethernet orSynchronous Optical Networking (SONET)/Synchronous Digital Hierarchy(SDH), that is different from the PON protocol used in the PON 100, theOLT 110 may comprise a converter that converts the network protocol intothe PON protocol. The OLT 110 converter may also convert the PONprotocol into the network protocol. The OLT 110 may be typically locatedat a central location, such as a central office, but may be located atother locations as well.

In an embodiment, the ONUs 120 may be any devices that are configured tocommunicate with the OLT 110 and a customer or user (not shown).Specifically, the ONUs 120 may act as an intermediary between the OLT110 and the customer. For instance, the ONUs 120 may forward datareceived from the OLT 110 to the customer, and forward data receivedfrom the customer onto the OLT 110. Although the specific configurationof the ONUs 120 may vary depending on the type of PON 100, in anembodiment, the ONUs 120 may comprise an optical transmitter configuredto send optical signals to the OLT 110 and an optical receiverconfigured to receive optical signals from the OLT 110. Additionally,the ONUs 120 may comprise a converter that converts the optical signalinto electrical signals for the customer, such as signals in theEthernet protocol, and a second transmitter and/or receiver that maysend and/or receive the electrical signals to a customer device. In someembodiments, ONUs 120 and optical network terminals (ONTs) are similar,and thus the terms are used interchangeably herein. The ONUs may betypically located at distributed locations, such as the customerpremises, but may be located at other locations as well.

In an embodiment, the ODN 130 may be a data distribution system, whichmay comprise optical fiber cables, couplers, splitters, distributors,and/or other equipment. In an embodiment, the optical fiber cables,couplers, splitters, distributors, and/or other equipment may be passiveoptical components. Specifically, the optical fiber cables, couplers,splitters, distributors, and/or other equipment may be components thatdo not require any power to distribute data signals between the OLT 110and the ONUs 120. Alternatively, the ODN 130 may comprise one or aplurality of processing equipment, such as optical amplifiers. The ODN130 may typically extend from the OLT 110 to the ONUs 120 in a branchingconfiguration as shown in FIG. 1, but may be alternatively configured inany other point-to-multi-point configuration.

In an embodiment, the OLT 110, the ONUs 120, or both may be configuredto implement an FEC scheme to control or reduce transmission errors. Aspart of the FEC scheme, the data may be combined with an errorcorrection code, which may comprise redundant data, before beingtransmitted. For instance, the data and the error correction code may beencapsulated or framed into a FEC codeword, which may be received anddecoded by another PON component. In some embodiments, the FEC codewordmay comprise the error correction code and may be transmitted with thedata without modifying the data bits. When the error correction code isreceived, at least some of the errors in the transmitted data, such asbit errors, may be detected and corrected without the need to transmitadditional data. Transmitting the error correction code in addition tothe data may consume at least some of the channel bandwidth, and hencemay reduce the bandwidth available for data. However, the FEC scheme maybe used for error detection instead of a dedicated back-channel toreduce the error detection scheme complexity, cost, or both.

The FEC scheme may comprise a state machine model, which may be used tolock an FEC codeword, e.g. determine if a plurality of received blocksthat represent the FEC codeword are aligned appropriately or in acorrect sequence. Locking the FEC codeword or verifying the FEC blocks'alignment may be necessary to obtain the data and the error correctioncode correctly. For instance, the OLT 110, the ONUs 120, or both maycomprise an FEC processor, which may be hardware, such as a circuit, orsoftware that implements the state machine model. The FEC processor maybe coupled to the corresponding receivers and/or deframers at the OLT110 or the ONUs 120, and may use analog-to-digital conversion,modulation and demodulation, line coding and decoding, or combinationsthereof. The FEC codeword comprising the received blocks may also belocked at a memory location or buffer coupled to the FEC processor andthe receiver.

Typically, downstream data in PON systems may be transmitted in aplurality of GPON Transmission Container (GTC) frames, e.g. at a GTClayer, within a plurality of corresponding fixed time windows, e.g. ofabout 125 microseconds. A GTC frame may comprise a downstream PhysicalControl Block (PCBd) and a GTC payload (e.g. user data) that may notcomprise time or time of day (ToD) information. However, to establishPON transmissions synchronization, ToD information or any othersynchronization information may be needed in the transmitted frames. Inan embodiment, the OLT 110 may be configured to transmit ToD informationand/or any other synchronization information to the ONU(s) 120, forinstance in a downstream frame in a corresponding transmission window.The downstream frame may also support the FEC scheme for error detectionand correction. Accordingly, the transmission window may comprise FECcode words, which may comprise data and error correction code, and timeor ToD information. Specifically, the transmission window may comprisean integer multiple of FEC codewords and a plurality of extra oradditional bytes that may not be FEC encoded, and therefore may not behandled or protected from errors using the FEC scheme. The additional orextra bytes may be used to provide time (e.g. ToD) and/orsynchronization information for PON transmissions and may also compriseHEC encoding that may be used to detect and/or correct any errors in thesynchronization data.

For instance, the OLT 110 may transmit downstream data in a plurality ofXGPON Transmission Container (XGTC) frames within a corresponding timewindow of about 125 microseconds or any fixed length time window. TheXGTC frame (and the corresponding time window) may comprise a payloadthat comprises the FEC codewords, for example about 627 FEC codewordsusing Reed Solomon (RS) (248,x) FEC encoding (e.g. x is equal to about216 or about 232). Additionally, the XGTC frame (and the correspondingtime window) may comprise additional bytes (e.g. in the PCBd), e.g.about 24 bytes, that comprise synchronization and/or timesynchronization data and HEC encoding, as described in detail below.

FIG. 2 illustrates an embodiment of a frame 200, which may comprise FECencoded control and/or user data and non-FEC encoded synchronizationinformation. For instance, the frame 200 may correspond to a GTC or XGTCframe, e.g. downstream from the OLT 110 to an ONU 120, and may betransmitted within a fixed time window. The frame 200 may comprise afirst portion 210 and a second portion 211. The first portion 210 maycorrespond to a GTC or XGTC PCBd or header and may comprise time orsynchronization information, such as a PSync pattern, a ToD, other timeand/or frame synchronization information or combinations thereof.Specifically, the time or synchronization information may not be FECencoded and may be associated with HEC encoding in the first portion210, which may be used to detect/correct a plurality of bit errors thatmay occur in the first portion 210. The first portion 210 is describedin more detail below. In an embodiment, the frame 200 may correspond toa GTC or XGTC frame that is encoded using RS (248,x), and thus the firstportion 210 may comprise about 24 bytes. Although, the first portion 210precedes the second portion 211 in FIG. 2, in other embodiments, thefirst portion 210 may be located in other locations of the frame 200,such as subsequent to the second portion 211.

The second portion 211 may correspond to a GTC or XGTC payload and maycomprise a plurality of codewords that may be FEC encoded. For instance,the second portion 211 may comprise an integer multiple of FECcodewords. The GTC or XGTC payload may comprise a Payload Lengthdownstream (Plend) 212, an Upstream Bandwidth map (US BWmap) 214, atleast one Physical Layer Operations, an Administration and Maintenance(PLOAM) field 216, and a payload 218. The Plend 212 may comprise aplurality of subfields, including a B length (Blen) and a cyclicredundancy check (CRC). The Blen may indicate the length of the US BWmap214, e.g. in bytes. The CRC may be used to verify the presence of errorsin the received frame 200, e.g. at the ONU 120. For instance, the frame200 may be discarded when the CRC fails. In some PON systems thatsupport asynchronous transfer mode (ATM) communications, the subfieldsmay also include an A length (Alen) subfield that indicates the lengthof an ATM payload, which may comprise a portion of the frame 200. The USBWmap 214 may comprise an array of blocks or subfields, each of whichmay comprise a single bandwidth allocation to an individual TransmissionContainer (TC), which may be used for managing upstream bandwidthallocation in the GTC layer. The TC may be a transport entity in the GTClayer that may be configured to transfer higher-layer information froman input to an output, e.g., from the OLT to the ONU. Each block in theBWmap 214 may comprise a plurality of subfields, such as an Allocationidentifier (Alloc-ID), a Flags, a Start Time (SStart), a Stop Time(SStop), a CRC, or combinations thereof.

The PLOAM fields 216 may comprise a PLOAM message, which may be sentfrom the OLT to the ONU and include Operations, Administration andMaintenance (OAM) related alarms or threshold-crossing alerts triggeredby system events. The PLOAM field 216 may comprise a plurality ofsub-fields, such as an ONU identifier (ONU-ID), a message identifier(Message-ID), a message data, and a CRC. The ONU-ID may comprise anaddress, which may be assigned to one of the ONUs and may be used bythat ONU to detect its intended message. The Message-ID may indicate thetype of the PLOAM message and the message data may comprise the payloadof the PLOAM message. The CRC may be used to verify the presence oferrors in the received PLOAM message. For instance, the PLOAM messagemay be discarded when the CRC fails. The frame 200 may comprisedifferent PLOAMs 216 that correspond to different ONUs, which may beindicated by different ONU-IDs. The payload 218 may comprise broadcastdata (e.g. user data). For instance, the payload 218 may comprise a GPONEncapsulation Method (GEM) payload.

FIG. 3 illustrates an embodiment of a frame portion 300 that maycomprise non-FEC encoded synchronization information, such as in adownstream GTC or XGTC frame. For instance, the frame portion 300 maycorrespond to the first portion 210 of the frame 200. The frame portion300 may comprise a PSync field 311, a ToD in seconds (ToD-Sec) field315, and a ToD in nanoseconds (ToD-Nanosec) field 321. In an embodiment,the frame portion 300 may comprise about 24 bytes, where each of thePSync field 311, the ToD-Sec field 315, and the ToD in nanoseconds field321 may comprise about eight bytes. Further, each of the PSync field311, the ToD-Sec field 315, and the ToD-Nanosec field 321 may compriseHEC encoding that may be used to detect/correct errors in thecorresponding field.

The PSync field 311 may comprise a PSync pattern 312 and a HEC field314. The PSync pattern 312 may be used at an ONU, for instance at a dataframer coupled to a receiver, to detect the beginning of the downstreamframe portion 300 (or the frame 200) and establish synchronizationaccordingly. For example, the PSync pattern 312 may correspond to afixed pattern that may not be scrambled. The HEC field 314 may provideerror detection and correction for the PSync field 311. For example, theHEC 314 may comprise a plurality of bits that correspond to a Bose andRay-Chaudhuri (BCH) code with a generator polynomial and a single paritybit. In an embodiment, the PSync pattern 312 may comprise about 51 bitsand the HEC field 314 may comprise about 13 bits.

The ToD-Sec field 315 may comprise a Seconds field 316, a Reserved (Rev)field 318, and a second HEC field 320. The Seconds field 316 maycomprise an integer portion of the ToD associated with the frame inunits of seconds, and the Reserved field 318 may be reserved or may notbe used. The second HEC 320 may be configured substantially similar tothe HEC 314 and may provide error detection and correction for theToD-Sec field 315. In an embodiment, the Seconds field 316 may compriseabout 48 bits, the Reserved field 318 may comprise about three bits, andthe second HEC field 320 may comprise about 13 bits.

The ToD-Nanosec field 321 may comprise a Nanoseconds field 322, a secondReserved (Rev) field 324, and a third HEC field 326. The Nanosecondsfield 322 may comprise a fractional portion of the ToD associated withthe frame in units of nanoseconds, and the second Reserved field 324 maybe reserved or may not be used. The third HEC 326 may be configuredsubstantially similar to the HEC 314 and may provide error detection andcorrection for the ToD-Nanosec field 321. In an embodiment, theNanoseconds field 322 may comprise about 32 bits, the second Reservedfield 324 may comprise about 19 bits, and the third HEC field 326 maycomprise about 13 bits.

FIG. 4 illustrates another embodiment of a frame portion 400 that maycomprise non-FEC encoded synchronization information. For instance, theframe portion 400 may correspond to a PSBd in a downstream GTC or XGTCframe. The PSBd 410 may comprise a PSync pattern 412, a superframestructure 414, and a PON-ID structure 420. In an embodiment, the frameportion 200 or PSBd may comprise about 24 bytes, where each of the PSyncpattern 412, the superframe structure 414, and the PON-ID structure 420may comprise about eight bytes. Further, each of the superframestructure 414 and the PON-ID structure 420 may comprise HEC encodingthat may be used to detect/correct errors in the corresponding field.

The PSync pattern 412 may be used to detect the beginning of the PSBd inthe frame and may comprise about 64 bits. The PSync pattern 412 may beused by the ONU to align the frame at the downstream frame boundary. ThePSync pattern 412 may comprise a fixed pattern, such as 0xC5E5 1840 FD59BB49. The superframe structure 414 may comprise a superframe counter 416and a HEC code 418. The superframe counter 416 may correspond to themost significant about 51 bits of the superframe structure 414 and mayspecify a sequence of transmitted downstream frames. For each downstream(XGTC or GTC) frame, the superframe counter 416 may comprise a largervalue than the previous transmitted downstream frame. When thesuperframe counter 416 reaches a maximum value, a subsequent superframecounter 416 in a subsequent downstream frame may be set to about zero.The HEC code 418 may correspond to the least significant about 13 bitsof the superframe structure 414 and may be configured substantiallysimilar to the HEC fields described above. The HEC code 418 may be acombination of a BCH code that operates on about 63 initial bits of theframe header and a single parity bit.

The PON-ID structure 420 may comprise a PON-ID 422 and a second HEC code424. The PON-ID 422 may correspond to about 51 bits of the PON-IDstructure 420 and the HEC code may correspond to the remaining about 13bits. The PON-ID 422 may be set by the OLT and used by the ONU to detectprotection switching events or for security key generation. The secondHEC code 424 may be configured substantially similar to the HEC fieldsdescribed above. Specifically, the HEC code 418 may be used todetect/correct errors in the superframe counter 416 and the second HECcode 424 may be used to detect/correct errors in the PON-ID 422.

Since the synchronization information may be encapsulated in a pluralityof extra bytes in the downstream frames that may not be FEC encoded, theHEC code may be added to the synchronization information in the extrabytes, as described in the frame portion 300 or the frame portion 400,to provide sufficient or acceptable error detection/correctioncapability for the synchronization information at the ONU. This HECencoding scheme may provide efficient error detection/correction in aplurality of cases. For instance, when the ONU is in a fast-sleepingcontext, the ONU may re-lock every certain time period (e.g. every about10 microseconds) to the OLT. As such, multiple errors may occur in thenon-FEC encoded extra bytes (e.g. about 24 bytes) in case of falselocking. However, there may be a substantially high probability that theerrors are prevented or accounted for using the HEC encoding in theextra bytes.

For example, in the case of a bit error rate (BER) of about 1e−03 in thePON downstream transmission, a HEC code that comprises about 13 bitswithin a corresponding about eight bytes field in the downstream frame,such as the HEC fields described above, may be used to detect up toabout three bit errors and to correct up to about two bit errors in thecorresponding eight bytes field. In this case, the probability ofobtaining about three bit errors in a corresponding about eight bytefield after using the HEC scheme may be substantially small, e.g. equalto about 0.0039 percent. The three bit errors may be detected but maynot be corrected using the HEC scheme. Further, the probability ofobtaining about four bit errors or more in the corresponding about eightbytes field after using the HEC scheme may be equal to about 0.0001percent. However, the chances of obtaining about two error bits or lessusing the HEC scheme may be substantially high, e.g. equal to about99.996 percent. The two bit errors may be detected and corrected usingthe HEC scheme.

During the frame locking process, the frame may be validated efficientlywith at least about two correctable PSync patterns in the receivedframe. For instance, the ONU may successfully lock the downstream frameif at least about two PSync patterns, such as the PSync pattern 312,have been received and detected correctly, e.g. in two subsequent abouteight bytes fields. The probability of detecting two consecutive PSyncpatterns correctly using two corresponding HEC codes, such as in the HECfield 314, may be substantially high, e.g. equal to about 99.996 percentraised to the second power or about 99.992 percent (e.g. 99.996%̂2=99.992percent). Thus, using about 24 extra bytes that comprise HEC encoding,as described in FIGS. 2, 3, and 4 may enable the ONU to lock thedownstream frame successfully at a substantially high level of certainty(e.g. about 99.992 percent).

Further, the chance of establishing a false lock at the ONU may requiredetecting two subsequent PSync fields that comprise the same fixedpattern (e.g. comprise the same bit errors). Such a situation may mostlikely occur when there may be about four bit errors in both PSyncpatterns. The probability of receiving the same about four bits in twocorresponding about 64 bits (or the about 24 extra bytes in the frame)may be calculated by the binomial coefficient that is one out of64*63*62*61/(1*2*3*4) or about 1/635,376 percent. As such, the chance ofgetting two false PSync patterns may be equal to about 0.0001 percentraised to the second power or about 1e−12 percent. Thus, the chance ofestablishing a false lock may be about equal to the product(1/635376)×(1e−12) or about 5e−19 percent, which may be negligible. In arelatively fast-sleeping context of re-locking, e.g. about every tenmicroseconds, this situation may correspond to one false lock occurringevery about 1.7e16 seconds and may be tolerated.

FIG. 5 illustrates an embodiment of a synchronization state machine 500,which may be used, e.g. by the ONU, to synchronize a downstreamtransmitted frame, such as the frame 200. The synchronization statemachine 500 may use a PSync pattern in the downstream frame that may notbe FEC encoded, such as the PSync pattern 312 or the PSync pattern 412.The PSync pattern may be located in a portion of the downstream frame,such as the PSBd, the frame portion 300, or the first portion 210. Insome embodiments, the PSync pattern may be protected by a HEC code, suchas the HEC field 314.

The synchronization state machine 500 may be implemented by the ONU,e.g. using software, hardware, or both. The synchronization statemachine 500 may begin at a Hunt State 510, where a search for the PSyncpattern in all possible alignments (e.g. bit and/or byte alignments) maybe performed. If a correct PSync pattern is found, then thesynchronization state machine 500 may transition to a Pre-Sync State520, where a search for a second PSync pattern that follows the lastdetected PSync pattern by a fixed time length (e.g. by about 125microseconds) may be performed. If a second PSync pattern is not foundsuccessfully at the Pre-Sync State 520, then the synchronization statemachine 500 may return from the Pre-Sync State 520 back to the HuntState 510. If a second PSync pattern is found successfully at thePre-Sync State 520, then the synchronization state machine 500 maytransition to a Sync State 530. If the Sync State 530 is reached, thesynchronization state machine 500 may declare a successfulsynchronization of the downstream frame, and subsequently frameprocessing may begin. In an embodiment, if the ONU detects M consecutiveincorrect PSync fields or patterns (M is an integer), then thesynchronization state machine 500 may declare an unsuccessfulsynchronization of the downstream frame and return back to the HuntState 510. For instance, M may be equal to about five.

FIG. 6 illustrates an embodiment of a framing method 600, which may beused, e.g. by the OLT, for framing a downstream frame, such as a XGTC orGTC frame before sending the downstream frame to the ONU(s). Thedownstream frame may comprise control and/or user data that may be FECencoded and synchronization and/or time data that may not be FECencoded. However, at least some of the synchronization and/or time datamay be protected in the downstream frame using HEC code. At block 610,the control data, user data, or both (control/user data) may beencapsulated into an integer multiple of FEC codewords in the downstreamframe. For instance, the control/user data may be converted in to aplurality of FEC codewords that may be located in the XGTC or GTCpayload portion. For example, the control/user data may comprise thePlend, a plurality of PLOAM fields or messages, user payload, orcombinations thereof.

At block 620, the synchronization/time data and the corresponding HECcode may be encapsulated in a plurality of remaining bytes without FECencoding in the downstream frame. For instance, the synchronization datamay be located in the XGTC or GTC PCBd or PSBd portion. Thesynchronization/time data may comprise a plurality of synchronizationelements, such as a PSync pattern, a ToD, a PON ID, or combinationsthereof. The synchronization/time data may also comprise a correspondingHEC code or field for at least some of the synchronization/timeelements, such as the ToD, the PON ID, and/or the PSync pattern. Atblock 630, the FEC codewords that comprise the control/user data and theremaining bytes that comprise the synchronization/time data andcorresponding HEC code may be transmitted, e.g. to the ONU(s), in thedownstream frame. The method 600 may then end.

FIG. 7 illustrates an embodiment of an apparatus 700 that may beconfigured to implement the PON framing method 600. The apparatus maycomprise a processing unit 710 and a transmission unit 720 that may beconfigured to implement the method 600. For example, the processing unit710 and the transmission unit 720 may correspond to hardware, firmware,and/or software installed to run hardware. The processing unit 710 maybe configured to arrange control data, user data, or both into aplurality of FEC codewords in a downstream frame and arrangesynchronization information in a plurality of additional non-FEC encodedbytes in the downstream frame, such as described in steps 610 and 620above. The synchronization information may comprise the PSync field 311,the ToD-Sec field 315, and the ToD-Nanosec field 321. Alternatively, thesynchronization information may comprise the PSync pattern 412, thesuperframe structure 414, and the PON-ID structure 420. The processingunit 710 may then forward the FEC codewords and the additional non-FECencoded bytes to the transmission unit 720. The transmission unit 720may be configured to transmit the FEC codewords and the additionalnon-FEC encoded bytes in the downstream frame within a fixed timewindow, e.g. at about 125 microseconds. In other embodiments, theprocessing unit 710 and the transmission unit 720 may be combined into asingle component or may comprise a plurality of subcomponents that mayimplement the method 600.

The network components described above may be implemented on anygeneral-purpose network component, such as a computer or networkcomponent with sufficient processing power, memory resources, andnetwork throughput capability to handle the necessary workload placedupon it. FIG. 8 illustrates a typical, general-purpose network component800 suitable for implementing one or more embodiments of the componentsdisclosed herein. The network component 800 includes a processor 802(which may be referred to as a central processor unit or CPU) that is incommunication with memory devices including secondary storage 804, readonly memory (ROM) 806, random access memory (RAM) 808, input/output(I/O) devices 810, and network connectivity devices 812. The processor802 may be implemented as one or more CPU chips, or may be part of oneor more application specific integrated circuits (ASICs).

The secondary storage 804 is typically comprised of one or more diskdrives or tape drives and is used for non-volatile storage of data andas an over-flow data storage device if RAM 808 is not large enough tohold all working data. Secondary storage 804 may be used to storeprograms that are loaded into RAM 808 when such programs are selectedfor execution. The ROM 806 is used to store instructions and perhapsdata that are read during program execution. ROM 806 is a non-volatilememory device that typically has a small memory capacity relative to thelarger memory capacity of secondary storage 804. The RAM 808 is used tostore volatile data and perhaps to store instructions. Access to bothROM 806 and RAM 808 is typically faster than to secondary storage 804.

At least one embodiment is disclosed and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. Wherenumerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R₁, and an upper limit,R_(u), is disclosed, any number falling within the range is specificallydisclosed. In particular, the following numbers within the range arespecifically disclosed: R=R₁+k*(R_(u)−R₁), wherein k is a variableranging from 1 percent to 100 percent with a 1 percent increment, i.e.,k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97percent, 98 percent, 99 percent, or 100 percent. Moreover, any numericalrange defined by two R numbers as defined in the above is alsospecifically disclosed. Use of the term “optionally” with respect to anyelement of a claim means that the element is required, or alternatively,the element is not required, both alternatives being within the scope ofthe claim. Use of broader terms such as comprises, includes, and havingshould be understood to provide support for narrower terms such asconsisting of, consisting essentially of, and comprised substantiallyof. Accordingly, the scope of protection is not limited by thedescription set out above but is defined by the claims that follow, thatscope including all equivalents of the subject matter of the claims.Each and every claim is incorporated as further disclosure into thespecification and the claims are embodiment(s) of the presentdisclosure. The discussion of a reference in the disclosure is not anadmission that it is prior art, especially any reference that has apublication date after the priority date of this application. Thedisclosure of all patents, patent applications, and publications citedin the disclosure are hereby incorporated by reference, to the extentthat they provide exemplary, procedural, or other details supplementaryto the disclosure.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. An apparatus comprising: an optical line terminal(OLT) configured to couple to a plurality of optical network units(ONUs) and transmit a plurality of downstream frames to the ONUs,wherein each of the downstream frames comprises a plurality of forwarderror correction (FEC) codewords and a plurality of additional non-FECencoded bytes that comprise synchronization information and that are atleast partially protected by Header Error Control (HEC) code, whereinthe downstream frame is a 10 gigabit passive optical networktransmission container (XGTC) frame that comprises a downstream PhysicalSynchronization Block (PSBd) and a XGTC payload, wherein the PSBdcomprises 24 non-FEC encoded bytes, wherein the PSBd comprises thesynchronization information, and wherein the XGTC payload comprises theFEC codewords.
 2. The apparatus of claim 1, wherein each of thedownstream frames comprises an integer number of FEC codewords, andwherein the non-FEC encoded bytes are about 24 bytes long.
 3. Theapparatus of claim 2, wherein the synchronization information comprisesan eight-byte physical synchronization sequence, an eight-bytesuperframe structure, and an eight-byte Passive OpticalNetwork-identifier (PON-ID) structure.
 4. The apparatus of claim 3,wherein the HEC code comprises a 13 bit first HEC code and a 13 bitsecond HEC code, wherein the superframe structure comprises a 51 bitsuperframe counter and the first HEC code, wherein the PON-ID structurecomprises a 51 bit PON-ID and the second HEC code, wherein the first HECcode protects the superframe counter, and wherein the second HEC codeprotects the PON-ID.
 5. The apparatus of claim 4, wherein the physicalsynchronization sequence is not protected by any HEC code.
 6. Anapparatus comprising: an optical line terminal (OLT) configured tocouple to a plurality of optical network units (ONUs) and transmit aplurality of downstream frames to the ONUs, wherein each of thedownstream frames comprises a plurality of forward error correction(FEC) codewords and a plurality of additional non-FEC encoded bytes thatcomprise synchronization information and are at least partiallyprotected by Header Error Control (HEC) code, and wherein thesynchronization information comprises a physical synchronization (PSync)field, a time-of-day in seconds (ToD-Sec) field, and a time-of-day innanoseconds (ToD-Nanosec) field, and wherein each of the PSync field,the ToD-Sec field, and the TOD-Nanosec field has a length of eight bytesand is protected at least partially by HEC code.
 7. The apparatus ofclaim 6, wherein the Psync field comprises a 51 bit PSync sequence whichis protected by a first 13 bit HEC code, wherein the ToD-Sec fieldcomprises a 48 bit Seconds field, and a three bit reserved field, whichis protected by a second 13 bit HEC code, and wherein the ToD-Nanosecfield comprises a 32 bit nanoseconds field, and a 19 bit reserved field,which is protected by a third 13 bit HEC field.
 8. The apparatus ofclaim 6, wherein each of the downstream frames is transmitted within afixed time window, and wherein the number of FEC codewords is equal toabout 627 FEC codewords.
 9. The apparatus of claim 6, wherein the FECcodewords are encoded using a Reed Solomon (RS) (248,x) FEC encoding,where x is equal to about 216 or about
 232. 10. The apparatus of claim6, wherein the HEC code is a Bose and Ray-Chaudhuri (BCH) code with agenerator polynomial and a single parity bit.
 11. The apparatus of claim6, wherein the synchronization information is not protected by any HECcode.
 12. A method comprising: processing a physical layer (PHY) framecomprising a physical synchronization block (PSB) and a scrambled PHYframe payload, wherein the PSB comprises a physical synchronizationsequence (PSync), a superframe counter (SFC) structure, and a passiveoptical network identifier (PON-ID) structure, and wherein the scrambledPHY frame payload comprises a plurality of forward error correction(FEC) codewords, and wherein the FEC codewords comprise FEC data derivedfrom a 10-Gigabit-capable passive optical network (XG-PON) frame. 13.The method of claim 12, wherein the PSync contains a fixed 64-bitpattern that is used to achieve alignment of a PHY frame boundary. 14.The method of claim 13, wherein the SFC structure comprises a SFC and aheader error correction (HEC) field, wherein the SFC value in each PHYframe is incremented by one with respect to a previous PHY frame, andwherein the HEC field is a combination of a code operating on the SFCstructure.
 15. The method of claim 14, wherein the PON-ID structurecomprises a PON identifier and a second HEC field, wherein the PONidentifier is set by an optical line terminal (OLT) at its discretion,and wherein the second HEC field is a combination of the code operatingon the PON-ID structure.
 16. The method of claim 15, wherein the PSyncis 8 bytes long, wherein the superframe counter is 51 bits long, whereinthe HEC field is 13 bits long, wherein the PON identifier is 51 bitslong, and wherein the second HEC field is 13 bits long.
 17. The methodof claim 12, wherein the FEC codewords do not protect the PSB.
 18. Themethod of claim 12, wherein the PHY frame is processed by an opticalline terminal (OLT).
 19. The method of claim 12, wherein the PHY frameis processed by an optical network unit (ONU).